Network Intrusion Detection Signatures, Part Four

by Karen Kent Frederick

This is the fourth in a series of articles on understanding and developing signatures for network intrusion detection systems. In part one we discussed the basics of network IDS signatures and then took a closer look at signatures that focus on IP, TCP, UDP and ICMP header values. In the second installment we looked at some signature examples. In the previous article, we began to examine the topic of protocol analysis, which means that the intrusion detection system actually understands how various protocols, such as FTP, are supposed to work. In this article, we will continue to look at protocol analysis and how it can overcome attempts by attackers to obfuscate their exploits so that they cannot be detected by simple intrusion detection signature methods.